The invention relates to lift systems for raising and lowering window blinds that have lift cords such as pleated shades, roman shades and venetian blinds.
Venetian type blinds have a series of slats hung on ladders that extend from a headrail to a bottomrail. In most venetian blinds a pair of lift cords is provided each having one end attached to the bottomrail and then passing through elongated holes in the slats up to and through the headrail. When the lift cords are pulled downward the blind is raised and when the lift cords are released the blind is lowered. A cord lock is usually provided in the headrail through which the lift cords pass. The cord lock allows the user to maintain the blind in any desired position from fully raised to fully lowered. Pleated shades and roman shades are also raised and lowered by lift cords running from the bottom of the shade into a headrail. The cord lock system and other cord lift systems used in venetian blinds can also be used in pleated shades and roman shades. Another type of lift system for window blinds utilizes a take-up tube for each lift cord. These tubes are contained on a common shaft within the headrail. Each lift cord is attached to one end of a tube. The tubes are rotated to wind or unwind the lift cord around tubes. This system is generally known as a tube lift system. Some tube lift systems are operated by a continuous loop cord that passes over one end of the axle and extends from the headrail.
In recent years the art has been concerned that cords, particularly looped cords, pose a strangulation threat to children who may become entangled in the cords. Consequently, there has been much interest in cordless blinds. These blinds rely on electric motors or spring motors to raise and lower the lift cord. One common cordless blind simply contains a motor connected to a tube collection system within the headrail. Another cordless blind relies upon a constant force spring motor attached to a spool or spools on which the lift cords are collected. This type of cordless blind is disclosed by Coslett in U.S. Pat. No. 5,105,867 and by Kuhar in U.S. Pat. Nos. 5,482,100; 5,531,257 and 6,079,471.
Coslett discloses a sun shade having a series of blades connected together to form a serrated shape like a pleated shade. The upper blade is mounted within a hollow housing and the lower blade is secured to a plate member. A constant force spring plate is wound around a spring spool member and further engaged to an output spool, both of which are within a hollow handle secured to the hollow housing. A cord is connected to the output spool and passed from the handle through the housing and the blades and is connected to the plate member. Such a cording arrangement is similar to that of a lift cord in a pleated shade or venetian blind. The spring retains the blades in a folded closed position. When the shade is extended the spring exerts tension on the cord. Consequently, Coslett teaches the user to fix the plate member along one side of the window and to provide a hook to retain the hollow housing at the opposite side of the window when the shade is covering the window. Thus, Coslett""s shade can be in only one of two positions, fully extended to cover the window or fully retracted. Furthermore, Coslett""s blind is not suitable for installation in an orientation in which one rail is fixed at the top of the window frame as is done for most building windows. That is so because when the blind is fully retracted most people could not reach the handle to extend or close the blind without standing on a stool or ladder.
Kuhar discloses a cordless, balanced blind that contains at least one constant variable force spring motor in the headrail. The springs in these motors vary in thickness or in width along their length as they are wound around storage drums. A cord spool is coupled to one or more spring drums. The lift cords of the blind are wound about the spool. Thus, the spring winds or unwinds as the blind is raised or lowered. The difference in width or thickness of the spring compensates for the increasing weight of the blind on the cords as the window covering is raised and the decreasing weight as the blind is lowered. Kuhar teaches that much effort be made to select and couple the spring motor to the cords so that the bottomrail is balanced at any and every position. Kuhar further teaches that several spring motors may be coupled together.
Placing the spring motors in the headrail as taught by Kuhar requires that the headrail be tall enough and wide enough to accommodate the spring motors. Consequently, the headrail must be larger than would be required if no spring motors were in the headrail. If one placed the spring motors in the bottomrail, a smaller headrail could be used; however, the weight of the bottomrail would be increased. Increasing the weight of the bottomrail would make it much more expensive to balance the bottomrail in any and every position as Kuhar teaches is critical. Perhaps this could be accomplished with more or larger spring motors, but that would change the dynamics of the blind. For that reason one following the teachings of Kuhar would be lead away from putting spring motors in the bottomrail.
I provide a cordless blind containing one or more springs in the bottomrail of the blind. Preferably the spring is a constant force spring motor of the type disclosed by Coslett and Kuhar. The spring motor is connected to at least one cord collector in a manner to maintain tension on the cord collector. The tension causes the lift cords to be collected on the cord collector when the cord collector and the lift cords are free to move, thereby moving the bottomrail toward the headrail. I further provide a lock mechanism attached to the cord collector or the lift cords. The lock mechanism has a locked position wherein the lift cords are restrained from being collected on the cord collector and has an unlocked position that allows the cord collector and plurality of lift cords to move freely. I prefer that the lock mechanism be biased toward a locked position. However, a two position, i.e. locked or unlocked, lock mechanism could be used. I further prefer to provide a button on the bottomrail to operate the lock mechanism.
The cordless blind of the present invention is easy to operate. A user simply presses the button to release the lock and either pulls the bottomrail down or allows the spring motor to raise the bottomrail. When the button is released the lock engages if the lock is of the type that is biased to a locked position. If a two position lock is used the user presses the button, moves the bottomrail to a desired position and presses the button again to lock the lock mechanism. Because the lift cords and cord collector are no longer free to move, the bottomrail stays in the position where it was when the button was released.
This cordless blind could be a pleated shade, a cellular shade, a roman shade or a venetian blind. If the shade is a venetian blind I prefer to provide ladders in which the rails of the ladders are connected to form a continuous loop. Then the slats can be tilted with a conventional tilt mechanism in the headrail.